The invention relates to an implant for holding and/or forming a dental prosthesis or artificial finger joint.
A dental implant with an anchoring part intended to be anchored in a jaw bone is known from FIGS. 14 and 15 of U.S. Pat. No 4,447,209 A. This anchoring part has a generally cylindrical sleeve whose jacket surface is provided with axial ribs and furrows alternating along the circumference. These improve the transmission, between implant and bone, of forces directed transversely with respect to the axis of the sleeve, but they do not contribute in any appreciable way to the transmission of forces which are approximately axially parallel. The jacket of the sleeve is furthermore provided with holes. However, the many holes distributed along the entire axial extent of the implant section comprising ribs weaken the implant and increase its bending capacity. This is particularly the case if the cylindrical sleeve has only a small diameter. With such an implant, there is a considerable risk that the implant, under the effect of loads, will execute micro movements which destroy bone in the area surrounding the implant and thereby cause loosening of the implant. In addition, in the event of substantial loading, the implant can fracture at the holes located in the vicinity of the bone ridge.
An implant known from FR 2 084 522 A has a substantially conical anchoring part which, after extraction of a natural tooth, is inserted, with the thinner cone end forwards, into the freed alveolus of the jaw bone. The conical anchoring part is provided with protuberances. These are preferably inclined outward from the conical surface in the direction extending away from the thinner cone end and have a terminal surface at the end remote from the thinner end. By contrast, at their end situated nearer to the thinner cone end, they run out at least approximately to a point. Before insertion into bone, the conical anchoring parts are ground to adapt them to the individual shapes of the alveoli. This entails additional work and can also have the consequence that some of the protuberances are ground away. Because of the generally conical shape of the anchoring part, the cross-sectional shapes and cross-sectional dimensions of the protuberances in sections at right angles to the axis of the anchoring part are not constant along this axis. Accordingly, the apices, longitudinal surfaces and longitudinal edges of the protuberances are not parallel, or at least not all parallel, with the axis of the anchoring part. Moreover, the protuberances situated near the thinner cone end have smaller radial distances from the axis than do the protuberances more remote from the thinner cone end. For these reasons, upon insertion of an anchoring part into a bone, the protuberances can penetrate only with difficulty, or at most very slightly, into the bone material and they do not therefore provide stable anchoring immediately after insertion. In addition, the protuberances increase the torsional strength of the connection of the implant to the bone only slightly, even after fusion of the bone to the anchoring part. Since the protuberances have no terminal surfaces or at least no appreciable terminal surfaces at their ends situated nearer to the thinner cone end, they also contribute at most little to the transmission, from anchoring part to bone, of axially parallel pressure forces directed toward the thinner cone end.
Artificial finger joints with two pivotably connected implants or joint parts are also known. Each of these implants has an anchoring part and a joint head. When using the implant, the anchoring part is fitted in a bone of a finger. The anchoring part consists of a cylindrical pin with a smooth surface and therefore affords only a weak anchoring in the bone.
The invention is therefore based on the object of avoiding disadvantages of the known implants and of the making available an implant which, immediately after insertion into a bone, permits a stable connection to the latter. The implant according to the invention, at the latest after incorporation, into the bone or healing, can easily transmit forces to the bone, which are directed approximately transverse to the axis of the implant, and also forces which are approximately axial of the implant. The implant according to the invention is nevertheless sufficiently resistant to fracturing, even with a small diameter, and has sufficient and favorable flexural strength.
According to the invention, this object is achieved by an implant for at least one of holding and forming one of a dental prosthesis and an artificial finger joint, which includes an anchoring part for insertion into a bone that has a lower implant end, an upper implant end that is situated at least approximately level with a top of the bone when the anchoring part has been inserted into the bone, an axis, and a peripheral surface extending between the lower implant end and the upper implant end and surrounding the axis where the peripheral surface is a generally cylindrical section and has at least ten protuberances distributed around and projecting away from the axis along at least one of a helical winding and of a circle encompassing the axis. In addition, at least a majority of the protuberances are elongate in a direction parallel to said axis, and has two flanks, an apex, a protuberance end directed toward the lower implant end, and at the protuberance end, a terminal surface which forms with the axis an angle of at least 60xc2x0, and at least the apex of each protuberance is curved in a cross-section perpendicular to the axis and connects the two flanks of the respective protuberance smoothly and continuously to each other.
When the implant according to the invention is used parallel with the axis of the anchoring part, said anchoring part can be inserted into a substantially cylindrical hole of a bone in such a way that the protuberances in the cross section are pressed partially into the bone material, and accordingly bone material protrudes into the axial interspaces or furrows present between adjacent protuberances, and fills these preferably partially or, if appropriate, even completely. The bone material adjoining the anchoring part is slightly cut and/or compacted and the implant is pushed in. The compaction is particularly advantageous if the bone material adjoining the anchoring part consists partially relatively porous spongy substance. By means of the pressing-in during insertion of the implant, the anchoring part is immediately anchored in a fairly stable manner and thereby immediately acquires good stability, so-called primary stability. Upon incorporation, the bone material grows into each recess or groove present between protuberances axially spaced apart from each other. Moreover, the axial interspaces or furrows filled only partially with bone material, preferably immediately after the insertion of the implant, are filled completely with bone material upon incorporation. The implant is then anchored in a very stable manner in the bone and can transmit to the bone substantial forces approximately parallel with the axis and also substantial forces directed approximately transverse to the axis. The forces are in this case distributed fairly uniformly on a large surface area of the bone adjoining the implant. Thus, even in the event of substantial loading of the implant, it is possible to avoid excessive local stressing of the bone, which could cause absorption of bone material. The implant according to the invention can therefore also be anchored permanently.